This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this proposal is to collect high-resolution X-ray diffraction data for three different biomacromolecules that are relevant to biology and public health. Our first objective will be to learn the mode of metabolite recognition by a bacterial, PreQ1 riboswitch. Such information is essential to understand this novel gene regulatory paradigm, which may serve as an antimicrobial target. Previously we determined the structure of the PreQ1 riboswitch at SSRL and have now obtained new crystals grown in the presence of various metabolites that span a broad range of binding affinities (Kd = 5 nM to 500 nM). We are also investigating the mode of binding of the G-protein beta-gamma to various small molecules shown to affect cell signaling by our collaborator. These molecules are hypothesized to bind in a "hotspot" on the beta subunit. Our goal is to locate this molecules by difference Fourier techniques, which has implications for developing novel effectors of G-protein signaling. Finally, we are working to determine the crystal structure of the HIV-1 protein Vif in complex with components of the Cullin-RING ligase complex. This viral/host protein interaction has not been characterized at the molecular level. Our goal is to identify well-diffracting crystals in order to proceed with a structure determination. Our complex comprises two human proteins, EloB and EloC, as well as HIV-1 Vif.